It is well known in the art of sealing devices which have seal lips, to provide a sealing device which utilizes a seal lip formed of a rubber-like elastic material or a resin material such as PTFE (polytetrafluoroethylene). In a conventional sealing device where a seal lip formed only of a rubber-like elastic material is used, the seal lip may be damaged by contact with the fluid which is to be sealed, such as, oil or other chemicals. This may be very inconvenient. On the other hand, where a seal lip is used that is formed only of a resin material, the seal lip has the problem that the seal lip does not suitably follow-up the operation of a rotational shaft to be sealed due to a lack of elasticity of the resin of the seal lip and due to a leakage of fluid such as oil from a small gap.
The prior art has attempted to solve the aforementioned problems by providing a sealing device 100, as shown in FIG. 10, having only a resin seal lip 101, in which the elasticity of the resin seal lip 101 is improved.
In such a sealing device 100, the resin seal lip 101 has outer diameter side end portions 102 which are nip-supported by a pair of reinforcing rings 103 and 104. In order to improve the follow-up performance of the resin seal lip 101 to the rotation of the shaft and to prevent an oil leakage through the small gap, grooves 107 and 108 are formed so as to provide a bellows shape on the peripheral surfaces of the resin seal lip 101 on a side of the resin seal lip opposite the fluid to be sealed and on a side of the resin seal lip opposite a fluid side not to be sealed. These grooves 107 and 108 are formed by an upper die 111 and a lower die 112, as shown in FIG. 11, and are provided with mutually opposing projections 109 and 110 on the die's pressing surfaces so as to provide grooves 107 and 108 on the upper and lower surfaces of the seal lip 101 as shown in FIG. 12.
Although the resin seal lip 101 of the conventional sealing device 100 has improved elasticity, the improvement in the elasticity is limited. The resin seal lip 101 still does not have as much elasticity as that of the seal lip formed of the rubber-like elastic material.
Furthermore, a sealing device 400, such as is shown in FIG. 13, is also well known. The conventional sealing device 400 includes a resin liner 407 which is bonded on a sliding surface 405 of a seal lip 402 formed of a rubber-like elastic material extending from a seal body 401 to the side of the seal lip opposite the fluid side to be sealed. The sealing device 400 thereby provides the elasticity of the rubber-like elastic material and improves durability of the sliding surface. The liner 407 has a sliding surface 403 on which is formed a helical groove 403 having a pumping function.
In such a conventional sealing device 400, however, the unsolved problem is that oil leaks through the small gap between the resin liner 407 and the rotation shaft 406.
In order to prevent the problems encountered in both the above-described conventional sealing devices, there have been further proposed various sealing devices of a compound type. Compound type sealing devices have a combination of a seal lip formed of a rubber-like material and a seal lip formed of a resin material.
A conventional sealing device 300 of a compound type is shown in FIG. 14. The sealing device 300 is for sealing a gap between a housing 301 and a rotation shaft 302. The sealing device 300 has outer diameter side end portions of a seal lip 303 on the side of the seal lip opposite the fluid side to be sealed formed of the rubber-like elastic material, of a resin seal lip 304 disposed on an atmosphere side on the back surface side of the seal lip 303 and of a back-up ring 305 disposed on a further atmosphere side of the resin seal lip 304 are all assembled together into a recessed portion 307 of a fit ring 306.
In this type of the sealing device, however, the resin seal lip 304 interferes with the back surface of the seal lip 303 of the rubber-like elastic material, providing the problem that there is poor follow-up performance of the resin seal lip 304 to the swing-rotation of the rotation shaft 302. Additionally, this type of sealing device is costly to assemble due to the requirement of m any assembling processes and many workings involved.
On the other hand, a sealing device 200, such as is shown in FIG. 15, is one provided with a resin seal lip 203 formed of the rubber-like elastic material which are integrally formed for eliminating the assembling processes such as mentioned above in the former example of FIG. 14. That is, the sealing device 200 is one for sealing the gap between a housing 201 and a rotation shaft 202. A reinforcing ring 205 is interposed between the rubber seal lip 203 on the side of the seal lip opposite the fluid side to be sealed and the resin seal lip 204 on the atmosphere side, and the rubber seal lip 203 is bonded integrally with the resin seal lip 204 through a plurality of perforations 206 formed in the reinforcing ring 205.
Furthermore, a back-up ring 207 is press-fitted to an inner periphery of the reinforcing ring 205 on the atmosphere side of the resin seal lip 204 to hold the resin seal lip 204 between the reinforcing ring 205 and the back-up ring 207.
FIG. 16 illustrates manufacturing processes of the aforementioned integral-compound type sealing device.
That is, a resin material 204A for forming a resin seal lip 204 is disposed in a mold cavity 507 of a rubber formation mold 506 constructed by upper first and second mold parts 501 and 502 and lower first, second and third mold parts 503, 504 and 505. The reinforcing ring 205 having the perforations 206 is disposed on the resin material 204A so as to abut against it, and under this state, a rubber material is vulcanized for forming the seal lip 203 of the rubber-like elastic material. Simultaneously with the formation of the rubber seal lip 203, the rubber material is backed integrally with a portion of the resin material 204A intruded into the cavity 507 and bonded thereto (refer to FIG. 16(a)).
Thereafter, as shown in FIG. 16(b), the upper first and second mold parts 501 and 502 are opened (in the direction of the arrow) to open the mold 506, and as shown in FIG. 16(c), the lower mold part 503 is pushed up in the direction of the arrow to form a lip front end portion. Then, as shown in FIG. 16(d), the lower second mold part 504, against which the resin material 204A abuts, is pushed up in the direction of the arrow, thereby separating the mold product from the mold 506.
However, even in the conventional compound type sealing device described above, a side of the lip facing radially inwardly, facing the shaft and the resin lip 204 of the seal lip 203 formed of the rubber-like elastic material is disposed adjacent to the resin seal lip 204, so that the resin seal lip 204 interferes with the rubber seal lip 203, thus providing the problem of poor follow-up performance with respect to the rotation shaft 202.
Furthermore, countermeasures for preventing the rubber material from rotating during manufacturing as well as the problems of dimensional performance in the formation of the resin seal lip 204 should be considered.
An object of the present invention is to solve the problems encountered in the prior art described above. A further object of the present invention is to provide a sealing device of a compound type having a combination of a seal lip formed of a rubber-like elastic material and a resin seal lip. A further object of the present invention is to provide a method of manufacturing the compound type sealing device capable of preventing the resin seal lip from interfering with the rubber seal lip. A further object of the present invention is to effectively prevent the rubber material from intruding during the manufacturing process. A further object of the present invention is to make the thickness of the resin seal lip relatively thin in order to improve the follow-up performance of the resin seal lip. A further object of the present invention is to reduce heat generation. A further object of the invention is to form the resin seal lip simultaneously with the rubber seal lip molding process.